1. Field of the Invention
This invention relates to a switching device of a type in which a moving contact is opened and closed with respect to a fixed contact by virtue of a snapping action of a movable member which is made of a plate spring.
2. Description of the Related Art
FIGS. 22 to 24 show, by way of example, a conventional microswitch which is used as a switching device for a window regulator in an automobile.
A movable member 1, made of a plate spring, includes a spring portion 2 which can be bent downwards, a substantially rectangular hole 3 formed around this spring portion 2, and arm portions 14. Formed in a free end portion of this movable member 1 is a moving contact 4. In a base end portion, the movable member 1 has a notched supporting point 5. A notched supporting point 6 is formed at a tip end of the spring portion 2. Formed upright in a case 7 is a terminal plate 10 having first and second support portions 8 and 9 which are spaced a predetermined distance apart. The case 7 further includes fixed contacts 11 and 12 facing each other in a vertical direction. The movable member 1 is arranged in the case 7, with the supporting point 5 in the base end portion thereof and the supporting point 6 at the tip of the spring portion 2 thereof being engaged with and supported by the first and second support portions 8 and 9, respectively.
In the state shown in FIG. 23, the free end portion of the movable member 1 is biased obliquely upwards by a displacing force due to a resilient force of the spring portion 2, and the upward component of the displacing force keeps the moving contact 4 in contact with the fixed contact 11 which is on a usually closed side of the case 7. When, in the state shown in FIG. 23, the base end portion of the movable member 1 is pressed downwards by an operating member 13, and the arm portions 14, 14 of the movable member 1 are brought to a position below the supporting point 6 of the spring portion 2, as shown in FIG. 24, the free end portion of the movable member 1 is biased obliquely downwards by a displacing force due to the resilient force of the spring portion 2, and the downward component of this displacing force causes the free end portion of the movable member 1 to move rapidly downwards, separating the moving contact 4 from the fixed contact 11 on the usually closed side, and bringing it into contact with the fixed contact 12 on a usually open side of the case 7. When the moving contact 4 is thus brought into contact with the fixed contact 12 on the usually open side, a motor of the window regulator is supplied with electricity, thereby causing a window to be raised or lowered.
In the above-described conventional structure, the moving contact 4 is brought into contact with the fixed contact 12 on the usually open side by virtue of a snapping action of the movable member 1. This snapping action can only be realized when movable member 1 is pressed by the operating member 13 to bring a portion of the movable member 1 adjacent to the second support portion 9 to a position below the supporting point 6 of the spring portion 2. As a result, the second support portion 9 in this state inevitably extends through the movable member 1. Hence the necessity for providing the hole 3 in the movable member 1. The problem with this structure is that the electric current to the motor of the window regulator must flow through the arm portions 14, 14 and the spring portion 2 of the movable member 1. Accordingly, the switch cannot have a large current capacity if the width of the arm sections 14, 14 is not sufficiently large. Consequently the width W of the movable member 1 must be relatively large. Furthermore, the width of the spring portion 2 must also be large if it is desired that the moving contact 4 be pressed against the fixed contacts 11 and 12 with a relatively high contact pressure. The movable member 1 will then be required to have a still larger width, resulting in an excessively large overall size.